Abstract. Last time we reported on Romeo, analyses with this tool were mostly based on translations to other tools. This new version provides an integrated TCTL model-checker and has gained in expressivity with the addition of parameters. Although there exists other tools to compute the state-space of stopwatch models, Romeo is the first one that performs TCTL model-checking on stopwatch models. Moreover, it is the first tool that performs TCTL model-checking on timed parametric models. Indeed, Romeo now features an efficient model-checking of time Petri nets using the Uppaal DBM Library, the model-checking of stopwatch Petri nets and parametric stopwatch Petri nets using the Parma Polyhedra Library and a graphical editor and simulator of these models. Furthermore, its audience has increased leading to several industrial contracts. This paper reports on these recent developments of Romeo.
In order to model resource-consumption or allocation problems in concurrent real-time systems, we propose an extension of time Petri nets (TPN) with a linear cost function and investigate the minimum/infimum cost reachability problem. We build on the good properties of the state class symbolic abstraction, which is coarse and requires no approximation (or k-extrapolation) to ensure finiteness, and extend this abstraction to symbolically compute the cost of a given sequence of transitions. We show how this can be done, both by using general convex polyhedra, but also using the more efficient Difference Bound Matrix (DBM) data structure. Both techniques can then be used to obtain a symbolic algorithm for minimum cost reachability in bounded time Petri nets with possibly negative costs (provided there are no negative cost cycles). We prove that this algorithm terminates in both cases by proving that it explores only a finite number of extended state classes for bounded TPN, without having to resort to a bounded clock hypothesis, or to an extra approximation/extrapolation operator. All this is implemented in our tool Romeo and we illustrate the usefulness of these results in a case study.
Abstract-Safety analysis in Systems Engineering (SE) processes, as usually implemented, rarely relies on formal methods such as model checking since such techniques, however powerful and mature, are deemed too complex for efficient use. This paper thus aims at improving the verification practice in SE design: considering the widely-used model of EFFBDs (Enhanced Function Flow Block Diagrams), it formally establishes its syntax and behavioral semantics. It also proposes a structural translation of EFFBDs to transition time Petri nets (TPNs); this translation is then proved to preserve the behavioral semantics (i.e. timed bisimilarity). After proving results on the boundedness of the resulting TPNs, it was possible to extend a number of fundamental properties (such as the decidability of liveness, state-access, etc.) from bounded TPNs to so-called bounded EFFBDs . Finally, these results led to both implementing and integrating a formal verification tool within a development platform for system design for defense applications and in which the underlying complexity is totally concealed from the end-user.
Verification is a key process in the dependability engineering of complex systems. As we have shown in earlier works, formal verification techniques such as model checking can be efficiently used in a Systems Engineering (SE) context, despite their inherent complexity. Considering the widely used Enhanced Function Flow Block Diagrams (EFFBDs), we have indeed developed a formal simulation and verification tool for these functional behavior models. Moreover, great care has been taken to conceal the processing complexity from the tool end-user. In this paper, we present our latest developments as well as an extension of both method and tool to the case of dysfunctional models, to take into account failures affecting the model elements. By addressing both fault removal and fault forecasting problems with formal methods, we thus hope to improve the dependability analysis practice in SE.
Although the eFFBD formalism dates back to the 1990s (or even, in a simplified form, the 1950s), it seems that it is still not as much used by the Systems Engineering community as it could. Indeed, eFFBD is a modeling language focusing on functional paradigm i.e. allowing functional and behavioral modeling and reasoning about a system. Currently, it is often confronted or compared to other languages such as SysML for activity modeling (activity diagrams) based on object paradigm. This paper aims to demonstrate the interest and the potential advantages for systems designers, like most of the discipline‐oriented designers to dispose of an enriched (conceptually and semantically) eFFBD modeling language called here xFFBD. This has to be a credible framework for modeling, communicating and reasoning about complex systems. After shortly recalling the history, the key concepts and capabilities of eFFBD, this paper compares eFFBD with other formalisms considered here as relevant for the study, Petri nets and SysML. Several leads are then identified and discussed in order to improve the eFFBD language and to provide a first draft version of xFFBD specification.
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